We are taking a wall out, it is stud but does support some weight. We are replacing the wall with a beam resting on a padstone in the outer wall and on a pillar at its other end. The engineer who drew up the modification a few years back suggested this pillar should be taken through the floor to the foundations. I have always had my suspicions about whether we'd find any foundations down there (kit house built 50 years ago) but looking through the original house plans has confirmed this:
"Foundations: Horizontal dpc min 150mm above ground level. External walls on concrete strip foundations size and depth to suit local site conditions. Any drainage beneath building to be encased in min 150mm concrete. Loadbearing internal partitions to bear on concrete oversite slab (thickened as necessary to suit local site conditions.)."
And also
"Ground floor 40mm sand / cement screed on 2 coats 'synthaprufe' on 100mm concrete slab on 1000g polythene damp proof membrane on blinding on min. 100mm hardcore. Level of concrete slab to be 150mm above surrounding ground (min)."
I am talking to professional and it looks like we'll have to add in some sort of foundations but I just thought I'd see if the forum could come up with some more imaginative solutions that involve less faff.. The load through the pillar is 1.25 tonnes, can we not just use some sort of steel plate (lost in the screed) to spread the load over a sufficient area of the existing 100mm slab.
Thanks
Slabs generally aren't designed to take load-bearing walls, posts etc (as confirmed by your engineer). If the slab hasn't been thickened locally to take the additional load then you usually have to either expose and use an existing footing or form a new one. I've never completed a domestic project (30 odd p/yr for the last 20 yrs) where the engineer or building control has allowed a load-bearing element to be constructed on a slab without some form of thickening/footing.
Do yourself a favour and speak to your local authority Building Control officer, it may save you an awful lot of money and put your mind at rest.
Your answer is going to be , cut a hole through the floor about 900mm square , fill it with concrete and put your pole ontop.. not a big job really, but is the only solution - from what I can see anyhow..
Agreed 100%. This could actually be done in a good day. Price of the concrete and spoils removal and labour. Sorted.Originally Posted by BCD
You need a decent piece of concrete underneath what you are proposing TBH.
We are mid way through a renovation and have had similar issues.
Dig out (900mm) mass fill and then build off it.
When you look long into an abyss, the abyss looks long into you.........
Of course, you have you hit decent ground at 900mm and there's actually no need to mass fill, that's just an expense on concrete.
Normally 600mm concrete depth would be sufficient off suitable sub strata.
Bearing in mind in doing this you'll have cut though your damp proof membrane. Talk to Building Control or a good Structural Engineer. A pad foundation as described above is likely what you need but consider all the issues such as DPM, cold bridging, etc.
I think the only way is has mentioned,digging a new foundation,as long as there's no surprises underneath you'll be fine ,easy enough to do yourself
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Thanks for your input folks. I am speaking to an experienced builder, an engineer and BC but just wanted to check there were no other options that we weren't seeing.
The weight you're describing sounds like the equivalent of a car. Could you park a car on the floor in question without damage? Almost certainly. The difference being that that car does not represent a single large point load, but four smaller ones.
I have to admit I'd be tempted to explore further the option of using a steel spreader plate.
I very much doubt any Building Inspector worth his weight in Sea Dwellers would buy that for a dollar.
Previously the same load was happily sitting on a stud wall...
But it may be a structural ie loadbearing stud wall. If there are timbers forming triangulations then the chances are it is.
The engineer described it as semi-load bearing, without it the floor upstairs would sag and bounce.
As someone with an engineering background I think the steel plate idea has merit, however if it is not accepted practice I suspect the chances of getting approval from BC are low, and that (along with getting the work done with minimal disruption) is the goal.
You miss the point. Intentional pun as this is about point loading as I see it.
If the floor plate of the former stud wall presented a surface area of X and the OP's proposed spreader plate presents a surface area of X I wouldn't lose sleep.
A piece of 1/2" steel plate would do the trick I would think.
You're right, I had missed that point although it wasn't exactly clear.
I also agree that a floor plate should do the trick but the size of the plate may be larger or smaller than the floor plate of the stud wall dependent on relative weights of the beam and the wall structure it's replacing.
Whether building control will accept that is another matter....
Last edited by Dave+63; 22nd September 2017 at 17:53.
This
Existing contact point probably 100mm x 5000 so I guess we'd be looking at a plate about 70cm square. I'll float it past BC, they are the boss.
Most engineers these days go over the top ,I've put steels in that I swear blind weighed more than they were carrying,I've taken timber lintels out that have been there 100 years and replaced them with concrete or steel ones ,be interested to hear the out come
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